Current steel production in the world is mostly based on integrated steel plants comprising blast furnaces and basic oxygen converters. Blast furnaces require coke which is prepared by carbonization of coal in coke ovens generally located close to the blast furnaces. These three units produce a considerable amount of surplus gases which are used for power generation or heating purposes in other areas of the steel plant, for example, blast air heating stoves, boilers, soaking pits, heat treating furnaces in rolling mills, and some plants burn the non-utilized portion in flare stacks.
Increasing prices for energy, mainly for coke, and environmental restrictions, related to CO2 emissions, have led to consideration of using available energies from integrated steelworks mainly for steel production instead of for power generation and other uses. Additionally, current increasing prices of scrap, DRI/HBI and other iron raw materials as well as the prevailing market fluctuations have generated a need of finding alternatives for the production of metallic iron at less cost by utilization of the chemical reducing potential of blast furnace gas (BFG), coke oven gas (COG) and blast oxygen furnace gas (BOFG).
Sometimes power generation does not fit the local electricity markets and these projects are not viable. Power generation also does not make optimum use of the chemical values of these gases. By incorporation of a direct reduction plant for reducing iron ores, the DRI produced with the COG and BOFG can be charged to the BF to decrease its consumption of coke and/or powdered coal injection (PCI), or alternatively, for increasing the production of hot metal with the same fossil fuels consumption, thus increasing the crude steel production of the integrated plant, as well as rendering the steel production facilities more environmentally fit by lowering the amount of CO2 released to the atmosphere per ton of steel. A further possibility is to increase the production of crude steel by melting the DRI with additional scrap in an electric arc furnace (EAF), without increasing the process capacity of BF and CO.
U.S. Pat. No. 4,889,323, the disclosure of which is hereby incorporated by reference for the teachings of process conditions therein, describes a mill arrangement for the production of steel wherein a direct reduction (DR) reactor is operated with a reducing gas prepared from an oxygen converter gas, off gas from the reduction reactor and coke oven gas. Coke oven gas is utilized after its fractionation by alternating pressure adsorption so as to increase its portion of hydrogen and lower its portion of hydrocarbons and also the COG is desulphurized and passed through a pressure swing adsorption (PSA) process. The reducing gas utilized in the reduction reactor is a mixture of the treated converter gas and the treated coke oven gas. DRI produced in the DR reactor is charged as coolant to the converter in substitution of steel scrap or to electric arc furnaces for the production of steel.
The process of this patent is addressed to the substitution of steel scrap charged to converters and does not teach or suggest either charging DRI to the blast furnace thus increasing the pig iron production, or the advantage of decreasing the specific amount per ton of steel of CO2 released to the atmosphere.
U.S. Pat. No. 4,822,411, the disclosure of which is hereby incorporated by reference for the teachings of process conditions therein, describes an arrangement of an integrated steel plant similar to that of the above-mentioned patent wherein a direct reduction plant is incorporated in the steel plant for the purpose of increasing the amount of steel produced without expansion of the capacities of the blast furnace and coking plant.
This patent suggests to increase the production of steel by charging the metallic iron obtained through the direct reduction reactor to the steel converters, while the amount of hot metal produced by the blast furnace remains the same. It also proposes to upgrade the reducing quality of coke oven gas by mixing it with gas from the oxygen converter and optionally with off-gas from the reduction reactor and reforming it in a catalytic reformer which is a huge piece of equipment implying high capital, operating and maintenance costs. This patent does not teach or suggest i) charging DRI to the blast furnace, thus increasing the pig iron production, ii) using the blast furnace gas for heating the reducing gas fed to the direct reduction reactor, or iii) the advantage of decreasing the specific amount per ton of steel of CO2 released to the atmosphere.
U.S. Pat. No. 4,248,624, the disclosure of which is hereby incorporated by reference for the teachings of process conditions therein, discloses a method for operating a blast furnace wherein a portion of a charge is pre-reduced iron ore with a relatively low metallization and a relatively high carbon content. This patent teaches using as a portion of the charge to a blast furnace, metallic iron as sponge iron, thus improving the productivity of the blast furnace and decreasing the specific coke rate. This patent does not suggest either the preparation of reducing gas for sponge iron production by combining coke oven gas and oxygen converter gas or the reduction of CO2 emissions per ton of steel as a consequence of charging pre-reduced materials to the blast furnace.